The present invention is concerned with video noise reduction systems which provide improved image quality on noisy pictures.
In known noise reduction systems for example as disclosed in British patent application No. 42751/76 (U.S. patent application Ser. No. 841,519) the noise reduction mechanism involves storing picture information from at least one field and using this stored information with incoming information to provide modified picture information, picture point by picture point, by adding together a portion of the stored information for the previous picture point with the same picture point from a current field. Because of the generally random nature of picture noise this process reduces the noise content. As this mechanism requires curtailing when any portion of the picture is moving relative to an earlier picture, there is a requirement generally to include a movement detector to control the degree of noise reduction applied to any particular picture point. In the aforementioned patent references, a mechanism for synthesising picture points from information from adjacent picture points is described for use in picture expansion or compression to provide the facility for picture zooming or standards conversion. The adjacent picture points may be from the same or different fields to provide area or volume manipulation. This manipulation may be adaptive so that the portions of adjacent picture point information used in the synthesis may be varied.
The present invention is concerned with extending the use of the adaptive volume manipulator to provide noise reduction. The noise reduction can take place at the same time as synthetic picture information is generated, for example, in a digital standards converter. Alternatively, the noise reduction may be used exclusively when there is no requirement for synthetic picture generation, for example in a digital synchronizer or a stand alone noise reducer system.